The present invention relates to a pre-mixing chamber for gas turbines.
As is known, gas turbines are machines which consist of a compressor, and of a turbine with one or more stages, wherein these components are connected to one another by a rotary shaft, and wherein a combustion chamber is provided between the compressor and the turbine.
Air is supplied to the compressor from the outer environment, in order to pressurise the compressor.
The compressed air passes through a series of pre-mixing chambers, which end in a nozzle or a converging portion, to each of which there is supplied fuel, which in the case of gaseous fuel is mixed with the air, in order to form an air-fuel mixture to be burned.
There is thus admitted into the combustion chamber, by means of one or more burners, which are supplied by a pressurised network, the fuel which is necessary in order to produce the combustion, which is designed to give rise to an increase in the temperature and enthalpy of the gas.
The known burner units have a complex structure, inside which, in the case of gaseous fuel, there is present an element in the shape of an ogive, which in turn is contained inside a body which ends in a converging portion, which in current technical language is generally known as a shroud, and is connected to a corresponding mouth, which permits connection of the shroud to the combustion chamber.
Corresponding turbulence in the flow of compressed air obtained from the compressor is created downstream from the element in the shape of an ogive, by associating with each burner an element, which is generally known according to the art as a swirler, which intercepts the flow of air obtained from the compressor, and is provided with a complex shape, consisting of two series of blades oriented in opposite directions, all of which is designed to produce this turbulence.
The turbulence thus created permits inter alia corresponding mixing of the air itself with the fuel, in the combustion chamber.
In order to improve the characteristics of stability of the flame, in the case of use of gaseous fuel, there is also generally provided a parallel fuel supply system, which can generate a pilot flame in the vicinity of the output of the burner.
The assembly constituted by these elements makes it possible to create a flame which has a substantially annular shape, and is positioned inside the combustion chamber, in the vicinity of the dome of the latter.
Finally, via corresponding pipes, the high-temperature, high-pressure gas reaches the various stages of the turbine, which transforms the enthalpy of the gas into mechanical energy which is available to a user.
If the area in which the combustion takes place is observed in greater detail, it can be noted that typically, in a position which is at the front in relation to the pre-mixing chamber, dynamic balance is created, which makes it possible to position the flame at an appropriate distance from the converging portion of the pre-mixing chamber.
This dynamic balance depends on various parameters, amongst which the characteristic air/fuel ratio of the mixture to be burned if of particular importance.
In fact, if the mixture is too rich, there is a faster speed of reaction, which however can cause a back-firing of the flame, which can give rise to destruction of, or damage to, the units of the gas turbine.
In addition, a rich mixture causes an undesirable increase in pollutant secondary combustion products, and in particular an increase in the nitric oxides (NOx).
However, it is not generally possible to increase the air/fuel ratio above a certain threshold, since this decreases the speed of reaction, and the flame withdraws from the burner, until undesirable extinction of the mixture takes place.
The object of the present invention is thus to eliminate the disadvantages of the known art, by providing a pre-mixing chamber or gas turbines, which makes it possible to reduce drastically the additional fuel required, thus rendering the pollutant emissions minimal, and which simultaneously keeps the main flame stable over a period of time.
Another object of the present invention is to provide a pre-mixing chamber for gas turbines which is safe and reliable, and is designed such as to obtain also a substantial energy saving compared with the known art.
A further object of the invention is to provide a pre-mixing chamber for gas turbines which is relatively simple and economical to produce, as a result of the advantages obtained.
These objects are achieved by a pre-mixing chamber for gas turbines, wherein the said gas turbine is of the type which comprises at least one compressor connected to the turbine, and comprises a combustion chamber, wherein the said pre-mixing chamber has a converging portion, positioned such as to give rise to combustion inside and said combustion chamber, and wherein the said pre-mixing chamber has a plurality of pipes provided with holes, which open into the combustion chamber, provided on a front portion of the said pre-mixing chamber, in order to generate a series of pilot flames, which are appropriately regulated, in order to stabilise a main flame, which is primed inside the combustion chamber, characterised in that a front area of the said converging portion of the pre-mixing chamber has at least one circular groove provided at the said holes which belong to the said pipes.
According to a preferred embodiment of the present invention, the circular groove has a cross-section substantially in the shape of a xe2x80x9cVxe2x80x9d.
According to another preferred embodiment of the present invention, at least one first surface which belongs to the converging portion has a partial protective coating, whereas a second surface of the converging portion, which also includes the V-shaped groove, is treated by means of a full protective coating.
According to another preferred embodiment of the present invention, the holes which belong to the pipes are disposed equidistantly in an annular direction, relative to a casing of the pre-mixing chamber.
According to a further preferred embodiment of the present invention, the converging portion of the pre-mixing chamber is connected in a detachable manner to the casing of the pre-mixing chamber itself.
Further alternative, preferred characteristics are described in dependent claims attached to the present patent application, to which reference is made for the sake of brevity.